Process of precipitating metals from solutions as sulphides



Feb. 24, 1931.

N. c. CHRISTENSEN 1,793,906

PROCESS OF PRECIPITATING METALS FROM SOLUTIONS AS SULPHIDES Filed May 3, 1926 M6 29 i f 1N VEN TOR.

phides by means of H S and CaCO be used with either chloride or sulphate solutionsbut is particularly applicable to chloride 1 solutions.

Patented Feb. 24, 1931 NIELS C. CHRISTENSEN, OF SALT LAKE CITY, UTAH PRooEss or PRECIPITATING METALS raom soriu'rxons AS sometimes Application filed May 3, 1926. Serial No. 106,567.

, This invention relates to processes for the precipitation of metals from solutions assul- It may J As noted in my U. S. patent application 66,400such metals as zinc, iron and manganese, the precipitated sulphides of which are soluble in dilute mineral acids, may

be precipitated from their chloride solutions a as sulphides by means of H S and calcium carbonate. As alsonoted in thispatent application, lead may also be precipitated as a sulphide from slightly acid brines in which the lead sulphide precipitateis soluble,

y means of H S and calcium carbonate.

3 also noted in the above'mentioned patent ap plication the precipitation of these sulphides may be made selective by the addition to the solution containingH S of the finely divided calcium carbonate in successive calculated ceedsas faras possible amounts,iPbS being precipitated first, ZnS second, FeS third and MnS last. In order to makeclean separate products certain precautions are necessary, particularly in theselective precipitation of the zinc, iron and manganese- To secure thebestresults the solution should containsuflicient H 8 at all times to maintain aslightly acid solution and the calcium carbonate and H S should be added together at such a rate that the acid is not neutralized to such a point that the sulphides other than the one which it is desired to precipitate are thrown down. For example if the zinc is being precipitated the solution should first be saturated with H 8 so that the reaction ZnCl +H S=ZnS+2HCl pro- (toward the right hand side of the equation). Then the H 8 and finely divided CaCO r should be added together (preferably in as near chemically equivalent amounts as possible), at such a rate as to maintain this original slightly acid condition as nearlyas possible, until the desired amount ofrzinc is precipitated. Durin the addition of the CaCO and H 8 the so ution should be vigorously agitated to prevent local concentration of CaCO sufficient to neutralize all the acid and allow precipitation of iron or manganese sulphides. The 0 (32100 neutralizes the acid to the point Where the zinc sulphide is precipitated as, indicated in the following equations:

2HCl+CaCO =CaCl f'H CO znet-l-n sanswnci If the proper conditions are maintainedns givenin the foregoing, practically all the zinc maybe precipitated in a pure condition, practically free i from iron or manganese. However in commercial operation the safest and probably the bestmethod would be to preclpitate most of the zinc and after filtering out theZnS,to precipitate a small middling product of mixed ZnS and FeS between the main zinc and iron precipitationsfl This middling precipitate may be utilized as such may be used to precipitate lead from the solu-t tion previous to thezinc precipitation or may be used to neutralize residual acid in the original solution Whichis to be treated. In either of the latter cases the zinc and iron are again brought into solution and may be recovered as pure products by subsequent precipitations. a a

After the precipitation of the zinc from thesolution or preferably after the middling product of mixed ZnS and FeS), the same precautions as above mentionedshould be taken in the precipitation of the iron. The 50 solution should preferably first be saturated WithH S s0 thatthe reaction a may proceed as far as possible (toward the right hand side of the equation). I-LS and CaCO are then added together (preferably in as near chemically equivalent amounts as possible, or preferably with an excess of H 8),

7 product may be secured.

' small amount of @2160 as at such a rate as to maintain as nearly as pos sible the acid condition at the beginning or" the iron precipitation, until the iron is all precipitated. In practical operation it would zinc precipitation.

in the same Way as the miXedZnS-FeS mid-,-

dling' precipitate. The. precipitated ZnS,

FeS and MnS willprecipitate lead from solution or neutralize the acid in, the original solution as indicated below 2HCl+FeS =reo1. +'n,'s

. Mas MnGh In'this "way the "metals in the middling product may be returned'to solution and all the'Zn, e and Mn may be recovered as pure products.

After precipitation ofthe Fe S (or prefer- 1 ablyiaztter the'middling product) thev Mn may beprecipitated by continued addition or CaCO and H S as described orniay beprecipitated by means of Ca(OH) and H 5 or with CatSH) 2 if application :Serial No. 66,400 mentioned ',above.

I It should be noted in connection with the precipitation of the metals asdescribed above, that the conditions during precipitation will vary with the character of the solutions. For

.example the reaction proceeds farther (toward the right) in a rather dilute Water solution of ZnCl -than in a concentrated sodium or calcium chlorlde;

brine containingZnGh. With the former the reaction may proceed until an ac1dconcentration in solut1on near 0.6% 1s reached wh-ilefin a concentrated brine the-reaction will proceed only to a-point where between 0.2%

, and 0.3%. acid concentration is reachedin solution. ,During the iron precipitation the maximum acid concentration which may be reached in the solution is much less than in the I 7 case of the z nc precip tation, and the concentration which may be, reached-during the Mn precipitation isless than in the case 01"- the ironprecipitation. To secure the same grade or precipitate relatively greater care in the addition of reagents so as to maintain proper conditions is'necessary with the iron than the zinc precipitation. If'th-e proper.

desired as noted in 'U. S.

conditions are maintained the zinc may be secured as a beautiful pure white precipitate of ZnS, the iron as a pure coal black precipitate of FeS and the manganese as a pure orange colored precipitate of Mus.

Inorder to secure pure precipitates and rapid precipitation pure finely divided CaCO is necessary. Also in order to secure satisfactory results the H S must be pure and relatively concentrated. A pure finely pulverized limestone may be used but pure precipitated GaGO is more satisfactory.:- Pure H S gas is also much preferable to a gas dilute with air or CD At first glanceit may appear to be practically impossibleto operate under these conditions as the H S is constant ly contaminated with CO -lrom;thereaction which takes place during precipitation. It would also appear that the use of pure precipitated CaCO would be too expensive for many practical operations. The control and storage of H S generated in such processesgas those described in my .U. S. Patents'Nos'. 1,539,711, 1,539,712 and 1,539,714 and U: s.

' pa ent application'No. 66,400, in connection with which the process of precipitation llGlQHl described 'is designed'to be used also ap ars 71V 1.. ditlicultyr' I aim-however to overcome all these difficulties ,bymy preferred method and apparatus'for usein thisprocess of precipitation whether the process is'used' for either a simple or a selective precipitation; By'my preferred method otcarrying out my "process I aim to make a very efficient absorption or collection of the H 8 in such form that itjmay to be 'a matter of some be stored andused witha minimum'of ditficulty. I also'aim-to avoid any difiiculty due to dilution of H S with CO during the precipitation of the sulphides and at the same time to make the'pure precipitated CaCO which is, most desirable in the process. My preferred method'also makesit possible to always be sure of an amount of H S-inexcess'oi the chemical equivalent ofthe GaCO 1 used in the process. :It also prevents loss oiand obviates the necessity of continuous passage of new H S through the solution and reabsorption to eliminate the CO generated. My preferred method of utilizing my proc ess is carried out in a special apparatus which is simple and efficient and of very high ca pacity. i

i The first stepinmy preferred process consists in absorbing the H S (generated in the processes,describedin myU. S; Patents Nos. l,539,7l1,l,539,712 and 1,539,71 land my U. S. patentapplication No. 66,400 orfromother sources) lime emulsion (or with m a lime and Water) to form a calcium sulphydrate (021(81-1) solution. Mypr'eferred method or carrying out this step consists in passing the H S gas through a spray ofan emulsion of Ca(OH) 2 in water in such amanne'ras to absorb the H S most efliciently and secure a relatively concentrated Ga(SH) "solution. The apparatus whlch I prefer to usefor this purpose consists 'oi a rapidly revolving cylinder dipping slightly into the lime emulsion to be sprayed and enclosed in-"a housing through which the H S gases are passed. This apparatus forms a spray fromsuch emulsions with a minimum of power and with no difficulties such as those due to clogging of nozzles, or -filling of towers when attempting touse these with an einulsion. The apparatus and its methods of use are' described in my U. S. Patent 7 0. 1,462,363. In this absorption step of my process I prefer to passthe HgS gas through a series of such spray chambers counter current to the flow of Ca(OH) emulsion so as to secure the maximum absorption of H S and highestconcentration of Ca(SH) solution possible. Tl1e"Ca(SH) solution coming from the absorption apparatus should be liltered to remove the: residual silicafcalcium carbonate, alumina,magnesia etc., and the blackprecipitate of-FeS which is made/oven with the best grade lime from traces of iron in the limestone used in the manufacture of the Ca(OI-I) This pure solution will then contain practically nothing but Ca( SH and a small excess of H 8 and is ready for use in the second step ofmy process in which the precipitation of the sulphides and the precipitation of the OaCO are carried out.

The precipitation step ofmy process is cars 1 ried out asfollows: H S is passed into the 35 solution until the desired or necessary saturation is reached, thereafter I LS and CaCO;

are simultaneously added at the proper rate while the solution is being agitated. The

CO generated during the precipitation is passed intocalcium sulphydraw solution driving off H 8 and precipitating GaCO as indicated in the following chemical equation ,der as described above, is placed for spraying liquid into the space in the chamber above the liquid. The two spray chambers are connected at opposite ends by means of a suitable duct or pipe in which a fan is placed to continuously circulatethe gases through the stray in both chambers. In one of the compartments thesolution to be precipitated is placed and inthe other Ca (SH) is placed. 'l hes'prays are then placed in'operation and H s is then passed into theapjparatus until the metal solution is saturated to the point desired. CaCO preferably in an emulsion with water is thenslowly added to the metal solution causing the precipitation of the metal sulphide and the generation of: C02. The CO iscireulated into the other compartment of the apparatus (by means of the fan and pipe) and is absorbed in the Ca(SH)g solution precipitating GaCO and generating Hf; The H S thus generated is circu lated through the solution spray and is absorbed therein thus making up for the II S consumed in precipitating the metals and maintaining the required saturation of H S as CaCO is added to the metal solution.

Since twice as much H S as is necessary for generated by of the apparatus is considerably increased.

Ii desired the process may be conducted at ordinary pressure but thebest results arosecured by allowing the pressure to build up to at least two atmospheres so as to off-set the effect of thedilution with CO on the rate of absorption of H 8 and the strength of H iti solution obtainable.

i The foregoing brief description will be made clearerby reference to the accompanyingfldiagramof the apparatus. Figure (1) shows a vertical longitudinal section through the apparatus on the line AA of Fig. II and FigmlI shows a vertical section on the line B--B of Fig. I. As noted above the apparatus consists of a closed spray chamber (1) divided into two spray compartments (2) and (3) by the haiiles or eliminators (4;) and solution partition (5). In each of the comf partments (2) and is a rotor spray (6) which throws a spray of the solution con-v tained in thelower parts (7) and (8) of each of the compartments into the gas in the upper parts (9) and (10) of eachof the compartments. The gases in the apparatus are circulated through the spray in the two spray compartments through the pipe (11) and fan (12) as indicated by the arrows. The operation of the apparatus is as follows: The lower part (7) of one of the compartments (2) is filled with solution of themetal to be precipitated to the level of the lower part of the spray drum (6) so that the drum dips 1 slightly into the solution and the cylinder or rotor (6) is rotated at such a speed that the upperpart (9) of the chamber is filled with a spray of the desired kind (which is regulated by thespeed and depth of dipping into the solution). The lower part (8) "of the other Compartment (3) is filled (to the level of the lower part of the rotor (6) with CaKSI-ll and the rotor is revolved so that the upper part (1.0) of this compartment is filled with spray'of the Ca(SH) solution. H S is iii-- troducedinto the apparatus until the spaces (9.) and (10) are'filled with the gas and the solutions saturated. to the desired degree,

The gases in these compartments are circutormedas indicated below: I i

The CO thus liberated is passed through the spray ofGa SI-D solution in the other compartment (10) causing the precipitation oi CaGO and releasing H S as indicatedbelow Ca SH) 2+ oo.+ H2O CaCO +2ii.s

Thai-LS passes through the spray in the metal solutioncompartment '(a) maintaining the H saturation in this solution and furnishing H S 'foi' 'the precipitation of the metal sulphide'. By the addition'of the correct amount of Ca (SH) solution in compartmentl y'and oi CaGO emulsion in proper proportion to the solution to be precipitated in compartment (2) the precipita tion may be carried to any desired point.

The pressure of H 5 in the apparatus may be maintained at any desired amount by regu'a lating the amount of H 8 released as the precipitation' progresses; lVhen the precipitation is completed to the desired point the two solutions are run into separate tanks and the precipitated metal sulphide and precipitated CaCO are settled or filtered out; The CaCOg'iswashed to remove-any Ca (SH) 2 solution and is used in precipitating other metal sulphides as described.

After the removal of the precipitated metal sulphide by settling or filtration the solution maybe returned for the precipitation of other metals asdesoribed above in my selective process of precipitat on.

it will be apparent from the foregoing that by this method pure H S and pure CaC0 forthe precipitation are obtained and the difficulties (if-maintaining a sufficient satu- Y ration of H S. without loss or continued reflbSOlCPtlOll of H 3, is overcome and that the H 8 is obtained and used in a form most suitable for collection and storage. The advantag-es thus obtained will be apparent to chemists and metallurgists engaged in similar linesof work.

CaCO (preter- My method of precipitation asnotedabove may be used for solutions of any kindbut is especially suited for chloridejsolutions' as the -CaCl formed in solution during the operation may be Washed out of'the precipitated sulphide; if sulphatesolutions are precipitated the CaSO formed contaminates the precipitated sulphides and all the GaCO inay not be used up due tothe coating effect of the CaSO on the particles of CaCO i It is obvious that my process may be used i'or'the, precipitation from solution as sulphides of any metals Whose sulphides are soluble in slightly acid solutions, and therefore require the use of the CaCO together with the PLS in order to secure the precipitation of the metal sulphides. For example cop per cadmium and cobalt may be precipitated -from chloride solutions and brines by this process. a a

It is also obvious that a considerable variety of selective precipitations of sulphides other than those mentioned may be secured by my process of using 02100;; together with H S in order to-maintainthe proper conditionsofvery slight acidity to-secure selective precipitation of the sulphides. The great advantage of thissubstantially automatic methodof maintaining the proper acid conditions within the very narrow limits required for selective precipitz. ion will be apparent to all chemists and nietallurgis'ts. By the proper use of CaCO and H S metalsthe solubilities of whose precipitated sulphides diiier veryslightly in'the various solutions used may be selectively precipitated and separated fromweach'other as pure products, the slight difference in acid concentrationnecessary for this selective precipitation being by the proper use of the CaCOgand H S. By this means theinost diiiicult and delicate separations are made possible and in fact are made very simple by maintaining a sufficient saturation of H 8 and'by adding the'CaCO in such a manner as to avoid neutralizing the acid formed in solutionrto a degree which allows theprecipitation of thesulphides slightly more easily soluble than the one it is desired to precipitate first. This may'appear a delicate process but is in fact a simple matter as witness the selectiveor'diiierential precipitation of zinc, iron and manganese'described in the foregoing and also" described in my U. S. patent application No. 66,400. It is obviously impossible todescribe all the possible applications of my process or variations in the details of its'use and I do notdesire therefore to be limited entirely by the foregoing descriptionexcept as interpreted in the appended claims.-

Having described my process and preferred methods and apparatus for carrying it out what-l claim and desire to patent-is:

1; The process ofprecipitatingfrom solutions metals whose sulphides-are soluble-in automatically maintained saidreagents to said solution in the presence of the other in saidsolution. 2. The process of precipitating from chloride solutions metals whose sulphides are soluble in such solutions it slightly acid,

which consists in the simultaneous treatment of saidsolutions with CaCOgand H by adding one of said reagents tosaid solution in the presence of the other in said solution.

The process of precipitating from chloride brines metals. whose sulphides are soluble in such brines if slightly acid, which consists in the simultaneous treatment of said brines with CaCO and H S by adding one of said reagents to said solutions in the pres ence of the other in said solution.

4:. The process of precipitating from solutions metals whose sulphides are soluble in such solutions it slightly acid by simultaneous treatment of said solution with H 5 and caCO which consists in impregnating said solutions with H 8 and adding finely divided CaCO to said impregnated solution and thereby precipitating metals therefrom as sulphides.

5. The process of precipitating from solu tions metals whose sulphides are soluble in such solutions it slightly acid by sin1ultaneous treatment of said solutions with H S and CaCO which consists in impregnating said solutions with H S and adding CaUO and H S to said solutions and thereby precipitating metals therefrom as sulphides.

6. The process ofselectively precipitating from solutions metals whose sulphides are soluble in such solutions it slightly acid by simultaneous treatment of said solutions with H S and CaCO which consists in impregnating said solutions with H S and adding (laCO to said impregnated solution and thereby precipitating as a sulphide one of a number of metals dissolved in said solution.

7 The process of selectively precipitating from solutions metals whose sulphides are soluble in such solutions if slightly acid by simultaneous treatment of said solutions with A H S and CaCO which consists in impregnating said solutions with H 53 and adding CaCO and H S to said impregnated solution and thereby precipitating as a sulphide one of a number of metals contained in Sand solution.

8. The process of selectively precipitating from solutions metals whose sulphides are soluble insuch solutions it slightly acid by simultaneous treatment of said solutions with H S and GaCO which consists in saturating said solutions with H 5 and adding CaCOg to said saturated solutions and thereby precipitating as a sulphide one of a number of metals contained in said solution.

9. The process of selectively precipitating -tio.ns metals whose sulphides are from chloride brines metals whose sulphides are soluble in such brines if slightly acid by simultaneous treatment of said solutions with H 3 and CaCO which consists in impregnating said solutions with H S and adding CaCO to said impregnated solution and thereby precipitating as a sulphide one of a number of metals in said solution.

10. The process of selectively precipitating from chloride brines metals whose sulphides are soluble in suchbrines ii slightly acid by simultaneous treatment of said solutions with l-LS and CaGO which consists in impregnating said brines with H 8 and adding (laCO and ILS andthercbyprecipitating as a sulphide one of a number of metals contained in said solution.

l 11; The process of selectively precipitating tromchloride brines metals whosesulphides are soluble in such brines if slightly acid by simultaneous treatment of said solutions with H 8 and CaCO which consists in saturating said brines with and adding H S and GaCO thereto and thereby precipitating as a sulphide one of a number of metals contained in said brine.

12. The process of precipitating from solutions metals whose sulphides are soluble in chloride brines metals whose sulphides are soluble in such brinesil. slightly acid, which consists 1n treating said. solutions simultaneously with H S and (laCO and thereby precipitating metal from solution as a sal phide and forming CaCl and CO and treat ing Ca(SH) solution with said CO to form H S and CaCO and using said TLS and CaCO to precipitate more metal from solution as described.

14. The process of precipitating from solusoluble in such solutions it slightly acid, which consists in enclosing said metal solution and a Ca(SH) solution in separate portions of a closed chamber and forming separate sprays from said solutions in said chamber and circulating gases in said chamber through said sprays of said solutions and adding H 8 and CaCO to said metal. solution and thcrebyprecipitating metal from said solution as a sulphide and forming ClaCl and CO and )assing said CO into said spray of (lafiill) solution and thereby precipitating CaCO, and forming I'LS and passiu g said H S into said spray of metal solution and adding more CflCOg thereto and thereby precipitating more metalsas' sulphide, and usingsaid :pre- .ClPltZltGCl (la-CO3 together with H 8 to precipitate metals from solution as described.

The process of precipitating metals from solutions as-sulphides by simultaneous treatment of said solutions with H s and CaCO which consists in impregnating said solutions withHgS and adding H 8 and finely divided calciumcarbonate in substantially equivalent amounts so as to maintain the {acidity of SitlClSOldtlOll :at such a concentration as to allow the precipitation of said metals as sulphides.

16. The process of precipitating metals from chloride solutions as sulphides by simultaneous treatment of said solutions with 1-1 8 and CaCO which consists in impregnating said solutions with H 8 and adding H 'S and finely divided calcium carbonate in substantially equivalent amounts so as to maintain the acidity of said solution at 1 such a concentration as to allow the precipitation of said metals as sulphides.

17. The process of precipitating metals from chloride brines as sulphides by simultan-eons treatment of said solutions with H S and iGaCO which consists in impregnating said solutions with H S and adding'H S and a I finely divided calcium carbonate in substanill) tially equivalent amounts so as to maintain the acidity of said solution at such a concentration as to allow the precipitation of said metals as sulphides.

18. The process of selectively precipitating nating said solution with H S and-adding H28 and finely divided calcium carbonate in substantially equivalent amounts, and in amount substantially equivalent to the metal metals from solutions as sulphides by simultaneous treatment of .said solutions with l-LS and CaCOg which consists in 1mpreg- "nating said solution with H 8 and adding H S Land finely divided calcium carbonate 'in substantially equivalent amounts and in amount substantially equivalent to the metal to be precipitated and thereby maintaining the acidity of said solution at such a concentration as. to allow the precipitation of one of said metals in solution as a sulphide and prevent the precipitation of other metals in said solution.

19. The process of selectively precipitating metals from chloride solutions as'sulphides by simultaneous treatment of said so lutions with H S and CaCO which consists in impregnating said solution With H S and adding H 8 and finely divided calcium carbonate in substantially equivalent amounts and in amount substantially equivalent to the metal to be precipitated andthereby maintaining the acidity of said solution at such a concentration as to allow the precipitation of one of said metals in solution as a sulphide and prevent the precipitation of other metals in said solution.

20. The process of selectively precipitating metal from chloride brines as sulphides by simultaneous treatment of said solutions with H s and CaGO which consistsin impreg- 

